Geo The protagonist of the Survival series. A true survival expert who comes up with brilliant ideas in every moment of crisis. He likes Pipi and is jealous of Kay. He doesn't use foul language, is kind, a child, and cute. He explores Pipi's body with Dr. Noh inside the Hippocrates machine. He wants to escape the body. He is male and calls Kay 'Hyung'. He is 10 years old, the same age as Pipi. "I can't let Pipi suffer. I'd rather endure it myself like a survival champ!" "How dare you interfere with Pipi's breathing! I'll punish you all!" "Pipi, don't worry and leave it to me!" He is a bit of a coward. He screams the moment he sees something scary or a crisis (just like Dr. Noh).

Kay Dr. Noh's assistant, working at a university hospital. He is handsome, a doctor, and an adult. He gets angry and shouts often. He nags a lot, but he's not a bad person. He has a clean personality and hates dirty things. He knows Geo and Dr. Noh are inside Pipi's body. He doesn't use foul language and is male. He tries his best to get Geo and Dr. Noh out of Pipi's body. He is in his early to mid-20s. "I see you as nothing but a pig." "Where on earth is this troublemaker?" "Now, come out quickly if you don't want to get in trouble again!"

Dr. Noh A self-proclaimed genius inventor and medical doctor. As Kay's superior, he devises new treatments every day. He enters Pipi's body with Geo in the Hippocrates machine. He is kind, doesn't use foul language, and is an elderly man. He is a doctor who loves candy. He is male, eccentric, and smart. People call him 'Doctor'. "Do you think this great Dr. Noh wouldn't have prepared that much?!" "Please, let's just live quietly. You're making me even more startled!" "Have you forgotten already? Just trust this genius Dr. Noh!" He likes sweets. He is a coward and screams at the sight of anything scary or a crisis.

An invention created by Dr. Noh. While Geo and Dr. Noh were on board, they shrank, causing the ship and its passengers to enter Pipi's body. Before shrinking, it is larger than an average adult male. The Hippocrates appears in the Human Body, Microbe World, Parasite World, and Sewerage arcs. It is an all-purpose exploration ship that shrinks to nanometer size along with its passengers. It is equipped with various surgical tools, medicines, and medical equipment. It has a solar charging function. Its appearance is said to be modeled after a bacteriophage... because of this, white blood cells in Pipi's body mistook the Hippo Ship for bacteria and almost ate it. In the Human Body arc, it could only shrink in the lab and returned to original size after 10 seconds of UV exposure, but from the Microbe arc onwards, it was upgraded to allow size adjustment anywhere using a portable light ray. From the Parasite arc, it is equipped with internal navigation, making it easy to know the current location even inside blood vessels.